In internal-combustion engines of more recent design the cylinder valves have been operated by electromagnetic actuators instead of the classic cam shaft/push rod assembly which have long characterized valve control in internal-combustion engines. Such an electromagnetic actuator generally includes two spaced electromagnets between which an armature may be reciprocated by electromagnetic forces generated by the electromagnets which are supplied with current from a control device. The electromagnetic force exerted on the armature is counteracted by the force of resetting springs. The armature is coupled with the cylinder valve (engine valve) to cause motion thereof as the armature executes its reciprocating motion. Such an electromagnetic actuator is disclosed, for example, in U.S. Pat. No. 4,455,543.
Operating a cylinder valve by means of an electromagnetic actuator permits a freely variable control by an electronic control device as concerns the opening moment and the open period of the valve to correspond to momentary load requirements. In the design of the electromagnetic actuator, however, the spring/mass system composed of the armature, the cylinder valve and the resetting springs has to be considered as being a fixed predetermined magnitude as concerns the oscillation characteristics of the system.
Heretofore mechanical springs such as coil springs have been used as resetting springs which basically perform in a satisfactory manner.
Engines having electromagnetically controlled cylinder valves of the above type, however, need valve-accommodating pockets in the piston crown, since after a de-energization of the electromagnets, the cylinder valve assumes its position of rest in a half-open position because of the force equilibrium of the mechanical springs. Such a free valve motion ensures that the valves do not impact against the piston and thus cannot be damaged or destroyed. Such a free valve motion is furthermore needed to be able to start the oscillating motion of the cylinder valves upon engine start even if the associated piston is in its upper dead center position. The valve pockets in the piston crown, however, very significantly break up the evenness of the combustion chamber and therefore make difficult to optimally configure the combustion chamber in non-homogeneously driven, directly-injected Otto engines.